Adoptive transfer of donor leukocytes can induce remission n patients with CML and a fraction of patients with acute leukemia who relapse following an allogeneic HSC transplant. However, such infusions carry a significant risk of severe GvHD, particularly when lymphocytes from matched unrelated or HLA disparate related donors are used. Furthermore, donor leukocyte infusions have been relatively ineffective in the treatment of recurrent AML, ALL or CML in blast crisis. Over the last grant period, we have developed a dicistronic vector, termed NIT, which, when transduced into human T-cells directs the coexpression of a mutant of human nerve growth factor receptor (LNGFR) and HSV thymidine kinase. Techniques permitting efficient transduction of antigen-sensitized T-cells and the isolation of NIT+ cells expressing LNGFR at high purity have been developed and standardized. Transduced NIT+ cells express both LNGFR and HSV-TK over extended periods in vitro and in vivo and can be eradicated by exposure to 0.01m concentrations of ganciclovir. We now propose to evaluate new strategies for generating T-cells from HLA-matched donors reactive against host minor alloantigens or leukemia-associated antigens which, after transduction with the NIT vector, could be adoptively transferred to transplanted hosts to induce a controlled reversible GvL and (or GvH) reaction to eradicate residual AML, blast crisis, CML, or All and/or to suppress or eradicate host lymphoid and hematopoietic cells and thereby achieve engraftment. Under Specific Aim 1, we will compare and contrast the capacities of a) dendritic cells differentiated from host derived AML blasts or Ph+ CML blasts, b) host AML or CML blasts transduced to express the costimulatory molecule B7.1 and c) host-derived EBV transformed B-cells to stimulate the generation of HLA-matched donor-derived minor allo-antigens reactive as well as leukemia selected CD4+ and CD8+ T-cells. Under Specific Aim 2, we propose to establish and evaluate a battery of HLA-null 721.221 EBV LCL and murine 3T3 cells each transduced with retroviral vectors to express single HLA alleles and b2 microglobulin and immunogenic peptide (and in the case of 3T3 cells, the costimulatory molecule B7.1, LFA-1, ICAM-1), as artificial antigen presenting cells for generation of HLA-restricted donor T-cells against host HA-1 or H-Y minor alloantigen peptides or leuke-mia- associated WT-1 and bcr/abl peptides. Minor alloantigen and leukemia associated antigen specific NIT vector transduced T-cells will be tested for their anti-host and anti-leukemic activity and their in vivo sensitivity to ganciclovir in a pre-clinical SCID mouse-human xenograft model (Specific Aim 3). Results will be used to formulate phase I/II trials of NIT+ host minor alloantigen-specific and/or leukemia reactive donor T-cells for the treatment of patients relapsing with AML, ALL or blastic CML post transplant (Specific Aim 4).